Rollup merge of #74536 - Nicholas-Baron:master, r=joshtriplett
Rollup merge of #74536 - Nicholas-Baron:master, r=joshtriplett

fix documentation surrounding the `in` and `for` keywords

Addresses #74529

The `in` keyword incorrectly referenced the `Iterator` trait. This reference was changed to `IntoIterator` without changing the underlying link.

Additionally, the `IntoIterator` trait was referenced towards the end of the documentation for `for`. An additional reference was added earlier and broadened the existing documentation from any iterator to anything that can be turned into an iterator.

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust